With the development of large-scale integrated circuits (LSI), there has been a serious problem in the testing of these circuits. Because the components are so small and so close together, the introduction of any test equipment into the circuit would so strongly interfere with the characteristics of the circuit, that the test could not be effectively performed. Specifically, a mechanical probe which would be applied to at a point within an integrated circuit might add so much capacitance or "load up" the circuits so substantially, that the measurement would be meaningless. Furthermore, since the circuits may operate up to 400 MHz, the problem of creating a high impedance probe becomes even more accute at these higher frequencies.
The only prior art method known to be effective in making LSI measurements involves a stroboscopic effect and requires extremely expensive equipment. It uses an electron beam to indirectly measure currents within the circuit.
The present invention overcomes the problem of probe interference without the significant cost and complexity of existing methods.